As an information output apparatus in a word processor, a personal computer or a facsimile, for example, a recording apparatus for recording the desired information such as character or image on the sheet recording medium such as paper or film is employed. There are various methods for such recording apparatus, but among others, a method for forming the text or image on the recording medium by depositing the recording material on the recording medium has been widely put to practical use. A typical example of this method is an ink jet recording apparatus.
The ink jet recording apparatus employs a nozzle group in which a plurality of ink discharge openings (nozzles) capable of discharging the ink of the same color and same density are integrally arranged to increase the recording speed or improve the image quality. Further, for higher image quality, it may have a nozzle group in which the ink of the same color and different density can be discharged, or the ink of the same color and same density can be discharged at several stages of discharge amount.
In such an image forming apparatus, as means for converting the multi-value input image data into the binary image equivalent to a recording signal of dots (or the image taking two or more values and having a smaller number of gradations than the input number of gradations), there is an error diffusion method. This error diffusion method makes a pseudo gradation representation by diffusing a binarization error occurring in a certain pixel over plural following pixels.
With the above error diffusion method, an image processing method involving the dot arrangement control for the ink of the same color and different density or the ink of different color has been offered. For example, in the image processing method as disclosed in U.S. Pat. No. 3,208,777, when the ink dots of the same color and different density are arranged, the dot of higher density (referred to as a deep dot) is firstly arranged by the error diffusion method, and the output position of the deep dot is optimally decided. And the decided output position of the deep dot is reflected to the position calculation by the error diffusion method of the lower density dot (hereinafter referred to as a faint dot) by the error diffusion method. With this technique, the optimal arrangement position of the faint dot can be decided to resolve a density error caused by the deep dot.
Also, in Japanese Patent Application Laid-Open No. 2004-336570, it was disclosed that the pseudo gradation output values for forming a pseudo gradation image with plural kinds of dots were decided, based on the correlation of plural independent image data corresponding to plural kinds of dots.
However, with the method as described in U.S. Pat. No. 3,208,777, an arrangement of dots having higher priority is decided, the correction data for reflecting the arrangement is produced, the data of dots having next higher priority is corrected using the correction data, and the arrangement position is decided. That is, in order to decide the arrangement of dot in the next order, it is requisite to perform a process of producing the correction data based on the arrangement of dot in its upper order, and correcting the data of dot in the next order, whereby the process is complex and the processing time is increased.
Also, with the method as described in U.S. Pat. No. 3,208,777, the arrangement position is decided in the order from the dot of higher priority, and the arrangement of dot having the next priority is decided in consideration of the arrangement result, whereby the arrangement computation by error diffusion must be performed in the order for all the dots. That is, when there are n plane data in which the ink amount is specified for each of the density, color and dot diameter, the error diffusion processing must be necessarily performed by n times until the final dot position is obtained.
Also, the method as described in U.S. Pat. No. 3,208,777 is not said to be effective for processing the color material of the color of the same density and different color. For example, when two plane data of cyan and magenta of the same density are binarized, the position of any one color of cyan and magenta is optimally decided, but the position of the other color can not be optimally decided.
Further, with the method as described in Japanese Patent Application Laid-Open No. 2004-336570, the pseudo gradation output values are decided simultaneously for a plurality of planes using an LUT table, whereby there is no idea of priority order regarding the dot arrangement.